Fastener members, having a flange portion and a hollow sleeve portion with a flarable end, are known and are commonly referred as Tee-nuts, or rivet type Tee-nuts. Other Tee nuts are available in which the Tee nut is simply inserted into a workpiece and is retained therein by spikes formed around the flange. In this specification, the term "Tee-nut" is used to describe such fastener members, whether of the flarable type or the simple sleeve type.
Such Tee-nuts are usually formed of sheet metal, and provide a flange portion with a plurality of fastening teeth or prongs, and a threaded sleeve, all formed out of a single piece of sheet metal.
Typically such Tee-nuts are used, for example, in furniture frames, for fastening the components of the furniture together. They also have a variety of other uses, both in furniture and in many other industries.
U.S. Pat. No. 5,348,432 granted to Nagayama on Sep. 20, 1994 discloses a Tee-nut having a sleeve in the form of a hollow cylinder with a relatively thin-walled counterbored flarable end portion and a relatively thicker-walled threaded portion. The thin-walled flarable hollow sleeve end is formed by counter boring an internally threaded hollow sleeve. When flared outwardly, the thin-walled flarable counter-bored end has a tendency to split, and the thin walled portion has a tendency to collect wood chips internally in the threads, as the Tee nut is driven in to the work piece.
U.S. Pat. No. 5,618,144, inventor Volkmar W. Leistner, title Tee-nut with Enlarged Sleeve End, granted Apr. 8, 1997 and assigned to Sigma Tool & Machine a Partnership of Sigma Tool & Machine Limited and Sigma Fasteners Limited shows an improved form of Tee-nut with a flarable end. In this patent the Tee-nut sleeve is swaged out to enlarge its diameter, without intermediate reverse forming operations. However, these Tee-nuts require to be inserted into and through a bore in a wooden workpiece. The enlarged flarable leading end which was inserted first into the bore tended in some cases, since the leading end of the open bore tended to catch on the wood or tear particles of wood away. However these problems were unusual since the holes in the workpiece were larger than the sleeve diameter, so as to admit the enlarged swaged out leading end. Enlarging the diameter of the hole meant that the Tee nut sleeve must be securely flared so as to make a firm fit in the hole.
A further factor in the consideration of the manufacture of Tee nuts is that where the Tee nuts are intended to be used without flaring, it has been the practice to supply a simple Tee nut with a cylindrical sleeve, and where it was intended to flare the Tee nut then a special Tee nut of flarable design was provided instead. This may involve the user in buying and storing two different types of Tee nuts, depending upon which Tee nut was to be used. Clearly it is desirable to provide a Tee nut which is adaptable to both types of installation, if it should become necessary to use a non-flaring Tee nut in place of a flaring Tee nut, and vice versa. It is further desirable to provide a flarable Tee nut which does not require the drilling of an oversize hole, so that a greater thickness of workpiece material is left around the hole for reception of the prongs.
Conversely it is desirable to provide a Tee nut which has a capacity for insertion into a regular sized hole in a workpiece, and when inserted, producing a greater holding power than with conventional Tee nuts with regular cylindrical shaped sleeves.